atomic spectroscopy and the bohr model of the atom · bohr model • niels bohr developed model for...
TRANSCRIPT
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October 14, 2014
Atomic Spectroscopy and the Bohr Model of the Atom
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October 14, 2014
Exploration 1:Using the spectroscope, look outside. DO NOT TRY TO LOOK AT THE SUN. Bad for your eyes.
What do you see?
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Exploration 2:Using the spectroscope, we will now look at various gasses of elements.
What do you see?
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Exploration 3: Flame TestFollowing the procedures demonstrated, you will test 4 different substances in a flame.
What do you see?
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What is happening?
Work on POGIL to STOP sign on P.3.
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October 14, 2014
What do you know about light now?
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Light
• Light is a type of electromagnetic radiation that travels as a wave and can also act like a particle called a photon.> A photon is a discrete packet of light energy
Examples of EM radiation:• X-ray Gamma rays Radiowaves• Visible light UV Microwaves
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Wavelength
• Wavelength: Distance between wave crests. Measured in (m or nm)
symbol
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Frequency
• Frequency: How fast a wave oscillates. Number of wavelengths that pass through a given point per second. (Units in Hz or /s)
symbol
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Wave Speed
• Wave speed: how fast wave is traveling through space. Measured in m/s.> Regardless of wavelength or frequency, all EM
radiation travels at 3.00 x 108 m/s (speed of light)
symbol c
http://micro.magnet.fsu.edu/primer/lightandcolor/speedoflight.html
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There is a mathematical relationship between the wavelength and frequency of a wave.
• The longer the wavelength, the lower the frequency.• The shorter the wavelength, the higher the frequency.
=wavelength (m)speed of light
(m/s)
frequency (Hz)
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h = Planck's constant
= 6.626 x 10-34 J*s
Energy of Light
• Light energy comes in discrete packets called photons> light energy is quantized: you can only have
discrete amounts of light energy.
Ephoton= h
If you substitute =wavelength (m)speed of light
(m/s)
frequency (Hz) Ephoton= h*c
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October 14, 2014
Example 1:
• A red light has a wavelength of 660 nm. What is the frequency? (remember to convert nm to m first!)> What is the energy of the photon?
• A light has a frequency of 6.8 x 1015 Hz. What is the wavelength?> What is the energy of the photon?
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Light Through a Prism
• When light is passed through a prism, the color components of light can be separated.
https://www.e-education.psu.edu/astro801/content/l3_p3.htmlhttp://climate.psu.edu/data/frost/frosttraining.php
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Continuous Spectrum
• Continuous spectrum: Shows all of the wavelengths of light that are being emitted by white light.> Light separates into continuous array of colors.> White light is a mixture of all of the different
colors of light.
• long wavelength• low frequency• low energy
• short wavelength• high frequency• high energy ROY G BIV
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Emission Spectrum
• Emission spectrum: shows the specific frequencies of light emitted by an excited atom.> Atoms have a unique emission spectrum. Can be
identified by the light they emit.
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Bohr Model
• Scientists had a difficult time explaining emission spectra> Why were there specific lines of color instead of
all the colors?> Why were the colors always the same for a
specific element?
This guy had an idea!
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*Finish POGIIL*
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Bohr Model
• Niels Bohr developed model for the atom that explained the atomic spectra.> Electrons go around an atom's nucleus in circular
orbits.> Circular orbits are different distances from the
nucleus.> Energy of an electron depends on its distance
from the nucleus.
Planetary orbital model
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Bohr Model
• When an atom absorbs a photon of light, it is absorbing energy.> Absorption of a photon: low potential energy
electron becomes high potential energy electron.> Emission of a photon: A high potential energy
electron loses some of its energy, electron moves closer to nucleus
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October 14, 2014
Bohr Model
• Since light energy is quantized, the energy of an electron must also be quantized.> An electron can only have discrete amounts of
potential energy.> With in the atom, there are energy levels.
Electrons cannot be "inbetween" energy levels
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Think about a staircase:
http://www.physics.ucla.edu/k-6connection/forwpsa.htm
Just like you can't stand in between the steps, an electron can only be in an energy level, not in between.
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∆Eelectron = En-final – En-initial
• ∆Eelectron > 0 when increasing n• ∆Eelectron < 0 when decreasing n• |∆Eelectron| = Ephoton
Energy of an electron
En= -2.18 x 10-18 Jn2
n= principal quantum number
negative sign means energy of e- bound to nucleus is lower than if it were a free e-